Design And Implementation Of CE-OFDM System Based On USRP RIO Platform In Satellite-ground Links

With global coverage,high-speed transmission,task variety of space information network has become a new round of competition,The importance of data transmission between satellite-ground links is becoming increasingly significant.Multi-carrier modulation,with its high spectrum efficiency,strong anti-interference ability,flexible carrier distribution characteristics can provide support for satellite-ground communication tasks,thus has great potential.As one of the multi-carrier modulation schemes,Constant Envelope Orthofonal Frequency Division Multiplexing(CE-OFDM)modulation scheme inherits the advantages of OFDM modulation.At the same time,the Peak to Average Power Ratio(PAPR)is reduced to 0d B,which solves the problem of nonlinear distortion caused by high power output in the satellite-ground links.However,the limited hardware resources in the link and the severe Doppler effect still pose challenges to the design of the system.Thus,this paper focuses on the key issues that CE-OFDM systems face in the satellite-ground link scenario,and proposes a low-complexity enhanced receiver(ER)based joint Periodograms Null Subcarrier CFO Estimation(P-NSCE)recovers the signal to solve the problem,and completes the design of the CE-OFDM system and hardware implementation of the satellite.First of all,this paper introduces the CE-OFDM signal model,modulation method,system framework,key parameters and module algorithms,and does a bit error rate performance analysis and parameter selection of CE-OFDM systems under different channel conditions.In a certain range,the system performance increases with the increase of the base number and the modulation index.Under the large modulation index,the CEOFDM system can fully utilize the multipath diversity of the channel.Then,This paper starts from two key points of receiver design and estimation algorithm,to studies the signal recovery of CE-OFDM between satellite-ground links.According to the signal propagation characteristics of satellite-ground links,Corazza model is selected as the channel model,and the influence of phase deviation on the system is excluded.The classical Arctanger Receiver(AR)avoids the "phase blur" phenomenon at the expense of computing resources and space complexity.As one of the improved linear receivers,ER receiver is based on the Taylor series expansion of CE-OFDM signal.After linear operation on the real and virtual components of data,the third-order term is eliminated to approximate the original transmission signal.On the other hand,the NSCE algorithm uses the null subcarrier signal component as the a priori information to estimate the frequency offset value.However,the linear receiver ER will amplify the influence of the interference term,making the estimation interval of the algorithm smaller,thus resulting in an error level of the system bit error rate curve.On the basis of improving NSCE algorithm,this paper proposes P-NSCE algorithm by cascaded the period graph algorithm with large estimation range.The simulation results confirm the key parameters such as the pilot length and verify the feasibility of the P-NSCE estimation algorithm based on the low-complexity ER receiver.Provides support for low-complexity,high-precision,and wide-range signal recovery of CEOFDM systems under satellite-ground links.Finally,in order to verify the effect of the CE-OFDM system in the implementation of the project,the hardware platform is used to build the CE-OFDM system,and the upper computer boundary of waveform transmission of CE-OFDM system based on USRP-2943 R equipment is tested,and the bit error rate performance of different receivers is tested,which shows that the implementation scheme of the system is feasible.This paper focuses on the key issues that CE-OFDM systems face on satellite-toground links,the signal recovery algorithm based on low-complexity receiver frequency offset estimation algorithm is proposed to improve the design of the system,completed the theory simulation and the USRP RIO platform for the implementation,contributing to the research and development of satellite-ground CE-OFDM modulation scheme.